Strain-dependent multicolor mechanochromism of 3 <i>H</i> -bis-naphthopyran in solid polymeric materials

Multimodal mechanophores are important targets for the design of complex stress-sensing materials due to their multicolor mechanochromic properties, which potentially enable discrete visual outputs under varying levels of stress and/or strain. We have developed a novel 3<i>H</i>-bis-naphthopyran mechanophore that imbues solid polymeric materials with force-dependent colorimetric sensing capabilities. Polydimethylsiloxane (PDMS) elastomers incorporating a 3<i>H</i>-bis-naphthopyran crosslinker were synthesized and deformed under uniaxial tension. The relative distribution of two distinctly colored merocyanine dyes is systematically biased under varying levels of applied stress and/or strain, resulting in the appearance of distinct coloration, which is characterized by pronounced changes in visible absorption spectra. This work demonstrates that judiciously designed bis-naphthopyran mechanophores can function as force sensors that visually report on the magnitude of applied force in elastomeric materials.